FGFR4 and breast cancer: In contrast, in the FGFR4 gene, missense mutations Val550Glu and Asn535Lys occur in approximately 7–8% of rhabdomyosarcoma cases, causing autophosphorylation and constitutive activation of the kinase domain, and Tyr367Cys in the human breast cancer cell line, MDA-MB453, in which constitutive activation of the kinase domain causes receptor activation in a ligand-independent manner.